Charge Your Tesla With Solar Power – Even OffGrid!

A typical grid tied solar system will generate power for use in the home first, with extra power being sent back to the grid. However, if the power goes out, the solar power also shuts down. With a battery system your solar keeps working, and the hybrid inverter automatically switches from grid-tied to off-grid. Below details an installation we did in Virginia demonstrating the advantages of having batteries alongside solar.

This particular array is on a standalone structure. We install solar panels on rooftops, both metal and shingle, as well as on the ground, on barns or anywhere structurally capable of supporting the weight. This particular array consists of 27 SolarWorld 235w modules, with 26 electrically connected and a dummy/spare panel. The total DC capacity is 6.11kW.

The solar array is split into two strings, with each string feeding a Schneider MPPT charge controller.

The charge controllers feed a DEKA Unigy II battery bank. This industrial grade, American Made battery bank consists of 24 2v cells in a single string to create the 48vdc system. This is the most efficient way to wire up and utilize lead acid batteries and yields longest lifespan.

The main workhorse of the system is the hybrid inverter. This particular installation has been in service for some years and still carries the Xantrex branding, rather than Schneider. This inverter sells back extra power to the grid when it is operational, but if the grid fails, it becomes an off-grid system. It can also call for and fire up a generator should the batteries get low in off-grid mode.

A regular electric water heater draws a LOT of power and would require a large amount of battery capacity and inverter wattage to run. However in this case we have a heat pump water heater, which draws less than 1kW and can easily run on the battery system while the grid is down. Here we see a transfer switch so that if the grid goes off, the customer can disable the auxiliary heating elements and switch it over to the critical load panel.

But what if you have an electric car? Normally, while the utility grid is up it would be charged via a dedicated high capacity circuit. This power would be offset by the solar while the grid is up with a traditional grid-tied solar system.

But if the utility power fails, so would any grid-tied solar and the ability to charge the car.

For this scenario, we’ve installed a dedicated receptacle connected to the battery backup so that the client can charge their car, albeit more slowly, from the solar battery system.

You can see in the first photo, most of the solar is going back to grid. In the second photo, most is going into the car.

True independence! A car that charges for free, even without utility grid power and free hot water to boot, without the complexities of a solar thermal system.

Of course, a much larger solar and battery system could power the fast charge receptacle as well in the event of grid failure.

It is also possible for us to retrofit existing grid-tied solar systems with batteries and a generator.